DMC complex catalyst and process for its preparation

ABSTRACT

A process for the preparation of a DMC catalyst useful in the polymerization of alkylene oxides into polyether polyols, which process having the steps of (a combining an aqueous solution of a metal salt with an aqueous solution of a metal salt with an aqueous solution of a metal cyanide salt and reacting these solutions, wherein at least part of this reaction takes place in the presence of an organic complexing agent, thereby forming a dispersion of a solid DMC complex in an aqueous medium; (b) combining the dispersion obtained in step (a) with a liquid, which is essentially insoluble in water and which is capable of extracting the solid DMC complex formed in step (a) from the aqueous medium, and allowing a two-phase system to be formed consisting of a first aqueous layer and a layer containing the DMC complex and the liquid added; (c) removing the first aqueous layer; and (d) recovering the DMC catalyst from the layer containing the DMC catalyst.

FIELD OF THE INVENTION

The present invention relates to a double metal cyanide complex catalystand to a process for its preparation.

BACKGROUND OF THE INVENTION

Double metal cyanide DMC) compounds are well known catalysts for epoxidepolymerization, i.e. for polymerizing alkylene oxides like propyleneoxide and ethylene oxide to yield poly(alkylene oxide) polymers, alsoreferred to as polyether polyols. The catalysts are highly active, andgive polyether polyols that have low unsaturation compared with similarpolyols made using strong basis catalysts like potassium hydroxide.Conventional DMC catalysts are prepared by reacting aqueous solutions ofmetal salts and metal cyanide salts to form a precipitate of the DMCcompound. Beside for the preparation of polyether polyols the catalystscan be used to make a variety of polymer products, including polyesterpolyols and polyetherester polyols. The polyols can be used forpreparing polyurethanes by reacting them with polyisocyanates underappropriate conditions. Polyurethane products that can be made includepolyurethane coatings, elastomers, sealants, foams, and adhesives.

DMC catalysts are usually prepared in the presence of a low molecularweight organic complexing agent, typically an ether, such asdimethoxyethane (glyme), or an alcohol, such as tert-butyl alcohol. Thecomplexing agent favourably impacts the activity of the catalyst forepoxide polymerization. Other known complexing agents include ketones,esters, amides and ureas.

In one conventional preparation, aqueous solutions of zinc chloride andpotassium hexacyanocobaltate are combined. The resulting precipitate ofzinc hexacyano cobaltate is combined with an organic complexing agent.An excess of metal salt is often used in such preparation. For instance,in EP-A-555053 a process for making easily filterable DMC catalysts isdisclosed, wherein the order of reagent addition, the reactiontemperature, and the stoichiometric ratio of the reactants arecontrolled. EP-A-555053 discloses that at least a 100% stoichiometricexcess of the metal salt relative to the metal cyanide salt should beused. In the working examples dimethoxyethane is used as the organiccomplexing agent. Zinc hexacyanocobaltate catalysts prepared by thisprocedure generally have zinc chloride to zinc hexacyanocobaltate moleratios of about 0.6 or more.

Similarly, in EP-A-654302 a process for preparing substantiallyamorphous DMC catalysts is disclosed. These catalysts are preferablymade using a water-soluble aliphatic alcohol complexing agent, such astert-butyl alcohol. Again, an excess amount of metal salt is used tomake the catalyst. In this method it is essential that metal salt, metalcyanide salt and complexing agent are intimately mixed, e.g. by highshear stirring or homogenization; conventional mechanical stirring isinsufficient. Zinc hexacyanocobaltate catalysts described therein havemore than 0.2 moles of metal salt per mole of zinc hexacyanocobaltatepresent, typically more than 0.5 moles of metal salt per mole of zinchexacyano-cobaltate.

EP-A-755716 discloses two different methods for preparing crystallineDMC complex catalysts. In one method, the catalyst is made by using anexcess amount of the metal salt, but the excess is less than a 100%stoichiometric excess relative to the amount of metal cyanide salt. Theresulting catalyst contains less than about 0.2 moles of the metal saltper mole of DMC compound in the catalyst. In a second method, a largerexcess of the metal salt can be used, but the resulting catalyst issubsequently washed with a mixture of water and an organic complexingagent in a manner effective to produce a DMC catalyst that contains lessthan about 0.2 moles of the metal salt per mole of DMC compound in thecatalyst.

In WO-A-97/40086 a method for preparing DMC complex catalysts isdisclosed, wherein aqueous solutions of excess metal salt and metalcyanide salt are reacted in the presence of an organic complexing agentusing efficient mixing to form a slurry, combining the slurry with apolyether having a molecular weight less than 500 isolating thecatalyst, washing the catalyst with an aqueous solution containingadditional organic complexing agent and finally recovering the solid DMCcomplex catalyst. The polyether used suitably is a polyether polyol,such as polyethylene glycol. The final solid DMC catalyst contains 5 to80% by weight of polyether polyol

In EP-A-700949 a similar method as in WO-A-97/40086 is disclosed, thedifference being that a polyether (polyol) having a molecular weightgreater than 500 is used.

In the methods discussed the initial DMC complex is formed in an aqueousreaction medium. The metal salts used and the salt formed during thecomplex formation reaction are well soluble in water and hence will bepresent in the aqueous phase. Since these salts are generallydetrimental to the activity of the DMC complex catalyst, they need to beremoved before the DMC catalyst is actually used for catalysing anyalkoxylation reaction. For instance, assuming that zinc chloride is usedas the metal salt and potassium hexacyanocobaltate as the metal cyanidesalt, the unreacted zinc chloride and the potassium chloride formed inthe reaction between zinc chloride and potassium hexacyanocobaltatewould pose a problem, as they are detrimental to the activity of thefinal DMC catalyst. Hence, these salts must be removed as quantitativelyas possible, which is generally done by separating the DMC catalystparticles from the aqueous phase.

All methods discussed so far have in common that the separation of theDMC complex catalyst particles from the salts-containing aqueous phaseis rather cumbersome. For instance, in the working examples ofWO-A-97/40086 the separation of DMC complex catalyst from the aqueousphase involves centrifugation and decantation, techniques which are notvery practicable when to be used on an industrial scale. The separationused in the examples of EP-A-555053 involved filtration using ahorizontal basket centrifugal filter and a light weight nylon fabricfilter medium. Separation of the formed DMC catalyst particles in theworking examples of EP-A-654302 involves either centrifugation orfiltration, while in the examples of EP-A-755716 filtration is used. Itwill be understood that filtration is also not optimal for use on anindustrial scale, inter alia because of filter plugging problems thatare likely to occur. Moreover, the separation techniques used in theprior art processes discussed above are likely to result in some waterand hence some salts remaining in the product. This is undesired.

SUMMARY OF THE INVENTION

The present invention aims to provide a method for preparing a DMCcomplex catalyst, in which the separation from the aqueous phase of theDMC catalyst particles formed can be performed efficiently, smoothly andcleanly on an industrial scale without losing any catalytic activity.Accordingly, the method should result in a highly active DMC catalyst,or in other words, the method of the present invention should have nonegative effect of the activity of the DMC catalyst.

These and other objects have been achieved by a method wherein aspecific liquid is added after the formation of the DMC catalystparticles, which liquid effect a phase separation resulting in anaqueous (bottom) phase containing the salts and a catalyst-containingphase floating on the aqueous phase.

DETAILED DESCRIPTION OF THE INVENTION

Accordingly, the present invention relates to a process for thepreparation of a DMC catalyst, which process comprises the steps of

(a) combining an aqueous solution of a metal salt with an aqueoussolution of a metal cyanide salt and reacting these solutions, whereinat least part of this reaction takes place in the presence of an organiccomplexing agent, thereby forming a dispersion of a solid DMC complex inan aqueous medium;

(b) combining the dispersion obtained in step (a) with a liquid, whichis essentially insoluble in water and which is capable of extracting thesolid DMC complex formed in step (a) from the aqueous medium, andallowing a two-phase system to be formed consisting of a first aqueouslayer and a layer containing the DMC complex and the liquid added;

(c) removing the first aqueous layer; and

(d) recovering the DMC catalyst from the layer containing the DMCcatalyst.

In step (a) an aqueous solution of a metal salt is combined with anaqueous solution of a metal cyanide salt and these solutions arereacted, wherein at least part of this reaction takes place in thepresence of an organic complexing agent. The product obtained after step(a) is a dispersion of a solid DMC complex in an aqueous medium. Ingeneral, the expression “aqueous medium” as used in this connectionrefers to water and any additional substance (e.g. complexing agent)dissolved therein.

Step (a) can suitably be performed by mixing the metal salt solutionwith the aqueous solution of metal cyanide salt, while simultaneouslyadding organic complexing agent either as a separate stream (e.g. assuch or in admixture with water) or in admixture with on or both of theaqueous reactant streams, e.g. dissolved in the aqueous metal saltsolution. In this mode of operation the complete reaction between metalsalt and metal cyanide salt takes place in the presence of organiccomplexing agent. Alternatively, the addition of organic complexingagent is only started immediately after both aqueous reactant streamshave been combined. The organic complexing agent may suitably be addedas such or in admixture with water. In this mode of operation thecomplexing agent will be present during only part of the reactionbetween said reactant streams. Namely, as soon as metal salt and metalcyanide salt are contacted the formation of the DMC complex starts. Thiscan be seen from the instant formation of a precipitate upon startingthe addition of one reactant stream to the other. Thus, when theaddition of organic complexing agent only starts immediately after thefull amounts of metal salt solution and metal cyanide salt solution havebeen combined, part of the DMC complex formation has already takenplace. For the purpose of the present invention it was found very usefulwhen the complexing agent is added immediately after combining the metalsalt solution with the metal cyanide salt solution.

Suitable metal salts and metal cyanide salts are, for instance,described in EP-A-755716, the description of which is hereinincorporated by reference. Thus, suitable metal salts are water-solublesalts suitably having the formula M(X)_(n), in which M is selected fromthe Group consisting of Zn(II), Fe(II), Ni(II), Mn(II), Co(II), Sn(II),Pb(II), Fe(III), Mo(IV), Mo(VI), AI(III), V(V), V(IV), Sr(II), W(IV),W(VI), Cu(II), and Cr(III). More preferably, M is selected from theGroup consisting of Zn(II), Fe(II), Co(II), and Ni(II). In the formula,X is preferably an anion selected from the Group consisting of halide,hydroxide, sulfate, carbonate, cyanide, oxalate, thiocyanate,isocyanate, isothiocyanate, carboxylate, and nitrate. The value of nsatisfies the valency state of M and typically is from about 1 to about3. Examples of suitable metal salts include, but are not limited to,zinc chloride, zinc bromide, zinc acetate, zinc acetonylacetate, zincbenzoate, zinc nitrate, iron (II) chloride, iron (II) sulfate, iron (II)bromide, cobalt III) chloride, cobalt (II) thiocyanate, nickel (II)formate, nickel (II) nitrate, and the like, and mixtures thereof. Zinchalides, and particularly zinc chloride, are preferred.

The metal cyanide salt is a water-soluble metal cyanide salt preferablyhaving the general formula (Y)_(a)M′ (CN)_(b)(A)_(c) in which M′ isselected from the group consisting of Fe(II), Fe(III), Co(II), Co(III),Cr(II), Cr(III), Mn(II), Mn(III), Ir(III), Ni(II), Rh(III), Ru(II),V(IV), and V(V). More preferably, M′ is selected from the groupconsisting of Co(II), Co(III), Fe(II), Fe(III), Cr(III), Ir(III), andNi(II). The water-soluble metal cyanide salt can contain one or more ofthese metals. In the formula, Y is an alkali metal ion or alkaline earthmetal ion, such as lithium, sodium, potassium and calcium. A is an anionselected from the group consisting of halide, hydroxide, sulfate,carbonate, cyanide, oxalate, thiocyanate, isocyanate, isothiocyanate,carboxylate, and nitrate. Both a and b are integers greater than orequal to 1; c can be 0 or an integer; the sum of the charges of a, b,and c balances the charge of M′. Suitable water-soluble metal cyanidesalts include, for instance, potassium hexacyano-cobaltate(III),potassium hexacyanoferrate(II), potassium hexacyanoferrate(III), calciumhexacyanocobaltate(III) and lithium hexacyano-iridate(III).

The organic complexing agent used should generally be reasonably to wellsoluble in water. Suitable complexing agents are, for instance,disclosed in EP-A-555053, the descriptions thereof is hereinincorporated by reference in its entirety, and in general arewater-soluble heteroatom-containing organic compounds that can complexwith the double metal cyanide compound. Thus, suitable complexing agentsinclude alcohols, aldehydes, ketones, ethers, esters, amides, ureas,nitrites, sulfides, and mixtures thereof. Preferred complexing agentsare ethers like dimethoxy-ethane and diglyme and water-soluble aliphaticalcohols, such as ethanol, isopropyl alcohol, n-butyl alcohol(1-butanol), isobutyl alcohol (2-methyl-1-propanol), sec-butyl alcohol(2-butanol), and tert-butyl alcohol (2-methyl-2-propanol). Of these,dimethoxyethane and tert-butyl alcohol are most preferred.

Combining both aqueous reactant streams may be conducted by conventionalmixing techniques including mechanical stirring and ultrasonic mixing.Although applicable, it is not required that intimate mixing techniqueslike high shear stirring or homogenization are used. The reactionbetween metal salt and metal cyanide salt may be carried out at apressure of from about 0.5 to about 10 bar and a temperature of fromabout 0 to about 80° C. However, it is preferred that the reaction becarried out at mild conditions, i.e. a pressure of about 0.5 to about 2bar and a temperature of from about 10 to about 40° C.

After the reaction has taken place and a DMC compound has been formedthe extracting liquid is added to the reaction product of step (a).Typically the extracting liquid is added under stirring and stirring iscontinued until the liquid has been uniformly distributed through thereaction mixture. Stirring time is not critical and may suitably takefrom about 10 seconds up to about 2 hours. It is considered beneficialfrom a process economic view to keep the stirring time as short aspossible and therefore, stirring time will typically be from about 30seconds to about 30 minutes.

After the stirring has stopped the reaction mixture is allowedsufficient time to settle, i.e. sufficient time to separate into twophases: an aqueous bottom layer and a layer floating thereon containingthe DMC catalyst dispersed in the extracting liquid.

The amount of the extracting liquid added should be sufficient to effectphase separation. Accordingly, normally at least about 1% by weight,preferably at least about 2% by weight and more preferably at leastabout 3% by weight based on total weight of the reaction product of step(a) of extracting liquid are added. Any amount of extracting liquidabove the minimum amount required to effect phase separation can beused. The maximum amount will usually be determined by hardwareconstraints like volume of the reactor. Typically, however, the amountof extracting solvent added will not exceed about 50% by weight,suitably about 30% by weight and more suitably about 20% by weight basedon total weight of the reaction product of step (a). The addition issuitably carried out at a temperature of from about 0 to about 80° C.,suitably about 10 to about 50° C. The pressure may the same as duringthe reaction in step (a).

Suitable extracting liquids used in step (b) should in fact meet tworequirements: firstly it should be essentially insoluble in water andsecondly it must be capable of extracting the DMC complex from theaqueous phase. The latter requirement implies that the organiccomplexing agent used must have a preference for interacting with thisextracting liquid over the aqueous phase containing the dissolved salts.Namely, it is believed that the complexing agent interacts with theextracting liquid and in fact drags along the DMC complete from theaqueous phase into the phase formed by the extracting liquid. Theextracting liquid can, for instance, be an ester, a ketone, an ether, adiester, an alcohol, a di-alcohol, a (di)alkyl carbamate, a nitrile oran alkane.

Preferably, the extracting liquid used comprises a compound of thegeneral formula (I):

wherein:

R¹ represents hydrogen, an aryl group, a substituted or unsubstitutedC1-C10 alkyl group or a group R³—NH—,

R² represents hydrogen, an optionally halogenated C1-C10 alkyl group, agroup R³—NH—, a group —R⁴—C(O)O—R⁵ or a cyanide group,

R³ represents hydrogen or a C1-C10 alkyl group,

R⁴ represents a substituted or unsubstituted alkylene group having 2 to15 carbon atoms,

R⁵ represents hydrogen, a substituted or unsubstituted C1-C10 alkylgroup, and

n and m independently are 0 or 1.

In a first preferred embodiment in the general formula (I) R¹ representshydrogen, m=1, n=0 and R² represents a group —R⁴—OH with R⁴ representingan alkylene group having 3 to 10 carbon atoms. A specific example ofthis preferred compound includes 2-butyl-2-ethyl-1,3-propanediol.

In a second preferred embodiment of the present invention in the generalformula (I) R¹ and R² independently represent an alkyl group having 1 to5 carbon atoms, m=1 and n=0. Preferred examples of this embodiment arediethyl ether, methyl tert-butyl ether, di-isopropyl ether and dibutylether. Of these methyl tert-butyl ether is particularly preferred.

In a third preferred embodiment in the general formula (I) R¹ representsan alkyl group having 1 to 6 carbon atoms, m=1, n=1 and R² representshydrogen or an alkyl group having 1 to 6 carbon atoms or a group—R⁴—C(O)O—R⁵ with R⁴ being a substituted or unsubstituted alkylene grouphaving 3 to 15 carbon atoms and R⁵ being an alkyl group having 1 to 5carbon atoms. The group R⁴ may contain alicyclic, aliphatic (alkyl) orpolar substituents, like C1-C4 alkoxy groups. Suitably R is a1,3-propylene group with one or two substituents on the middle carbonatom. Preferred examples of this embodiment are ethyl formiate, ethylacetate, ethyl-2-ethyl-3-methyl butanoate, di-ethyl malonate anddi-ethyl 2-cyclohexyl-2-propyl malonate.

In a fourth preferred embodiment in the general formula. (I) R¹ and R²independently represent an alkyl group having 1 to 5 carbon atoms, m=0and n=0. Thus, in this embodiment the compound added in step (b) is analkane having from 2 to 10 carbon atoms. Heptane was found to beparticularly useful for the purpose of the present invention.

In a fifth preferred embodiment in the general formula (I) R¹ representsan aryl group, suitably a phenyl group, or an alkyl group having 1 to 5carbon atoms, R² represents a cyanide group, m=0 and n=0. Preferredexamples of this embodiment are benzonitrile and pivalonitrile(tert-butylnitrile).

In a sixth preferred embodiment R¹ and R² independently represent agroup R³—NH— with R³ being hydrogen or a C1-C10 alkyl group, m=0 andn=1. Preferred examples of this embodiment are butyl carbamate, dibutylcarbate and propyl carbamate.

In a seventh preferred embodiment R¹ represents hydrogen, R² representsa halogen-substituted C1-C5 alky group, m=0 and n=0. Preferred examplesof this embodiment are dichloromethane, 1,2-dichloroethane andtetrachloroethane.

In step (c) of the process of the present invention the aqueous layerformed is removed. Since the aqueous layer forms the bottom layer of thetwo phase system formed, this could e.g. be easily accomplished bydraining the aqueous layer via a valve in the bottom part of the vesselin which the phase separation occurred. In addition to water the aqueouslayer will typically contain the excess complexing agent used (i.e. thatamount of complexing agent which is not attached to the DMC complex),the water-soluble salts like the unreacted metal salt (e.g. zincchloride) and any water-soluble salt formed during the reaction betweenmetal salt and metal cyanide salt (e.g. potassium chloride and cobaltsalts) and possibly a small amount of the extracting compound left inthe aqueous phase. Normally the aqueous layer removed will constitutefrom 10 to 90 volume % of the total volume of liquid plus catalystparticles present in the vessel, but the volume ratio of aqueous layerto extracting compound layer is not critical for the workability of thepresent invention. The exact ratio will normally be determined byhardware constraints. After removal of the aqueous phase the remainingphase contains the solid DMC catalyst particles, which are dispersed orfinely divided in the extracting compound and which are subsequentlyrecovered in step (d).

The recovery step (d) may be carried out in various ways. As is alsodescribed in the patent specifications discussed herein before, suchrecovery procedure will normally involve mixing the DMC catalyst withcomplexing agent, optionally in admixture with water, and separating DMCcatalyst and complexing agent/water again, e.g. by filtration,centrifugation/decantation or flashing. This procedure may be repeatedone or more times. Eventually, the catalyst is dried and recovered as asolid. As disclosed in WO-A-97/40086 and EP-A-700949, the descriptionsthereof is herein incorporated by reference in its entirety, the finalsolid catalyst can also be recovered as a composition also containingfrom about 5 to about 80% by weight of polyether having a molecularweight of respectively less than 500 and greater than 500. Step (d) ofthe present process suitably comprises adding a water/complexing agentto the DMC catalyst layer and admixing catalyst layer andwater/complexing agent (e.g. by stirring), allowing a two-phase systemto be formed and removing the aqueous layer. This procedure may berepeated one to five times after which the remaining catalyst layer maybe dried and the catalyst may be recovered in solid form (as a powder)or, alternatively, a liquid polyether polyol may be added to thecatalyst layer and a catalyst suspension in polyether polyol is formed,which can be used as such.

In one embodiment a preferred recovery step (d) comprises the steps of

(d1) admixing organic complexing agent, water and optionally additionalextracting liquid with the layer containing the DMC catalyst andallowing a two phase system to be formed consisting of a second aqueouslayer and a layer containing the DMC catalyst;

(d2) removing the second aqueous layer;

(d3) optionally repeating steps (d1) and (d2) one to five times,suitably one or two times;

(d4) adding organic complexing agent to layer containing the DMCcatalyst while stirring; and

(d5) removing the complexing agent (e.g. by flashing or stripping) andrecovering the DMC catalyst as solid particles.

In another embodiment the recovery step (d) comprises steps (d1) to (d4)as defined above followed by:

(d5) adding a liquid polyol to the product of step (d4), thereby forminga slurry of DMC catalyst in a liquid medium of polyol/organic complexingagent;

(d6) removing the organic complexing agent; and

(d7) recovering the DMC catalyst as a suspension in the liquid polyol.

The amount of water used in step (d1) should be sufficient to form anaqueous layer. The organic complexing agent and water and optionallyadditional extracting liquid may be added as separate streams or as amixture in a single stream. Additional extracting liquid may be added tocompensate for any small amount left in the aqueous phase. If added, itwill be in small amounts. The weight ratio of complexing agent to watersuitably ranges from about 5:95 to about 50:50, more suitably from about10:90 to about 40:60. The total amount of water and complexing agentadded is not critical and could, for instance, correspond with up toabout 20 volume % more or less than the amount of aqueous layer drainedin step (c). Water and complexing agent are effectively admixed with theDMC catalyst layer, for instance by mechanical stirring. After effectivemixing has taken place the resulting mixture is allowed to settle, sothat a two phase system can be formed. Once this has happened theaqueous (bottom) layer is removed in step (d2). This can take place inthe same way as described supra for step (c). The procedure may berepeated one to five times, suitably one or two times.

In step (d4) pure organic complexing agent is added to the DMC catalystlayer while stirring in an amount which corresponds with the amount ofaqueous layer drained in the preceding step, although 20 volume % moreor less would still be acceptable.

In subsequent step (d5) the complexing agent may be removed by strippingor flashing, thus recovering the DMC catalyst as a solid. The complexingagent may, for instance, be flashed off at atmospheric conditions orunder reduced pressure. Flashing under reduced pressure is preferred,because this enables separation at a lower temperature which reduces therisk of thermal decomposition of the DMC catalyst. In a particularlypreferred embodiment the organic complexing agent is removed by flashingunder vacuum at a temperature of about 50 to about 80° C. Together withthe complexing agent traces of water and extracting liquid, which werestill present in the mixture are also removed. The DMC catalyst isrecovered as a solid and may be subjected to a subsequent dryingtreatment.

Alternatively, step (d5) comprises adding a polyol in an amountsufficient to form a catalyst slurry of DMC catalyst in a liquid mediumof polyol and complexing agent. Suitably, the amount of polyol is suchthat the solids content of slurry formed is from about 1 to about 50% byweight, more suitably from about 1 to about 30% by weight and mostsuitably from about 1 to about 10% by weight.

The polyol added may be any liquid polyol which is suitable to serve asa liquid medium for the DMC catalyst particles. Given the application ofthe DMC catalyst—catalysing the polymerisation of alkylene oxides intopolyether polyols—it is preferred to use a polyol which is compatiblewith the polyether polyols to be produced and which will not have anynegative effect on the final polyether polyol produced when beingpresent therein in trace amounts. Therefore, it is particularlypreferred to use a polyether polyol similar to the polyether polyol tobe produced by the DMC catalyst. Examples of suitable polyols thusinclude polyols such as polyethylene glycol, but preferred polyols arethe poly(alkylene oxide) polyols based on propylene oxide and/orethylene oxide similar to those envisaged for preparation using the DMCcatalyst.

In the subsequent step (d6) the organic complexing agent is removed fromthe catalyst slurry. This can be achieved by any means known in the artto be suitable for liquid-liquid separation. A preferred method for thepurpose of the present invention is flashing off the complexing agent atatmospheric conditions or under reduced pressure. Flashing under reducedpressure is preferred, because this enables separation at a lowertemperature which reduces the risk of thermal decomposition of the DMCcatalyst. In a particularly preferred embodiment the organic complexingagent is removed by flashing under vacuum at a temperature of about 50to about 80° C. Together with the complexing agent traces of water andextracting liquid, which were still present in the mixture are alsoremoved.

Finally, in step (d7) the DMC catalyst is recovered as a slurry inpolyol. The advantage of such a slurry is that it is storage stable andcan, for instance, be stored in a drum. Moreover, dosing of the catalystand its distribution through the polymerization medium is greatlyfacilitated by using a catalyst slurry.

In a further aspect the present invention also relates to a catalystobtainable by the process as described herein before.

In a final aspect the present invention also relates to a process forthe polymerization of an alkylene oxide, which process comprisespolymerising an alkylene oxide in the presence of the DMC catalyst and ahydroxyl group-containing initiator. Preferred alkylene oxides areethylene oxide, propylene oxide, butene oxides, styrene oxide, and thelike, and mixtures thereof. The process can be used to makehomopolymers, random copolymers or block copolymers.

The DMC catalysts of the invention are very active and hence exhibithigh polymerization rates. They are sufficiently active to allow theiruse at very low concentrations, such as about 25 ppm or less. At suchlow concentrations, the catalyst can often be left in the polyetherpolyol without an adverse effect on product quality. The ability toleave catalysts in the polyol is an important advantage becausecommercial polyols currently require a catalyst removal step.

Polyether polyols prepared using the DMC catalyst prepared in accordancewith the present invention have a very low unsaturation, namelyconsistently less than about 0.007 meq/g and even less than about 0.005meq/g. Such low unsaturation offers advantages for polyurethanes madewith the polyols of the invention.

Polyether polyols made with the catalysts of the invention suitably havea nominal average functionality of from about 2 to about 8, moresuitably from about 2 to about 6. The polyols may have a number averagemolecular weight up to about 50,000, but typically the molecular weightis within the range of about 500 to about 12,000, more typically fromabout 2,000 to about 8,000.

The invention will be further illustrated by the following examples,however, without limiting the invention to these specific embodiments.

EXAMPLE 1 Preparation of DMC Catalyst

Procedure A: An aqueous zinc chloride solution (30 grams in 100 mlwater) was added to a one liter glass reactor equipped with a mechanicalstirrer. An aqueous solution of potassium hexacyanocobaltate (12 gramsin 225 ml water) was added under stirring in 30 minutes. Immediatelyafter all potassium hexacyanocobaltate was added a mixture of water (95grams) and tert-butyl alcohol (117 grams) was added under stirring.Stirring was continued for another 30 minutes and the mixture wasallowed to stand overnight resulting in a viscous, white coloured,stable dispersion of DMC complex particles in a water/tert-butyl alcoholphase.

Procedure B: To the dispersion obtained after Procedure A was addedmethyl tert-butyl ether (70 grams) under stirring. Stirring wascontinued for another 5 minutes. After the stirring had stopped twodistinct layers were formed: a highly viscous, white coloured upperlayer and a transparent, water-thin, bottom layer. After draining thebottom layer (337 grams), 337 grams of a 25/75 m/m tert-butylalcohol/water was added under stirring. After stirring for an additional5 minutes followed by settling during 30 minutes the transparent bottomlayer was drained again. This layer had a mass of 355 grams.Subsequently, 355 grams of a 25/75 m/m mixture of tert-butyl alcohol andwater was added together with 15 grams of methyl tert-butyl ether understirring. After stirring for an additional 5 minutes followed bysettling during 30 minutes the transparent bottom layer was drainedagain. The drained layer had a mass of 308 grams. Then, 308 grams oftert-butyl alcohol was added under stirring followed by 240 grams of apropylene oxide adduct of glycerol having a number average molecularweight of 670 Dalton (G670). After stirring for a further 30 minutes thetert-butyl alcohol and residual water were removed by stripping underreduced pressure (300 mbar) a 60° C. until the water content of theDMC/G670 mixture was less than 0.5 wt %.

The product was a highly viscous, stable, white coloured dispersioncontaining 5 wt % DMC catalyst particles dispersed in G670.

EXAMPLE 2 Polyol Preparation

A one liter mechanically stirred reactor was charged with 89 grams ofG670 and 160 milligrams of the DMC catalyst dispersion prepared inExample 1 (corresponding with 20 ppm DMC catalyst based on endproduct).Traces of water were removed by heating the resulting mixture to 130° C.at 5 mbar. The pressure was subsequently released to 50 mbar withnitrogen, after which propylene oxide was added until the pressure was1.1 bara (corresponding wit) 6 grams of propylene oxide). Then theremaining 305 grams of propylene oxide were added while the pressure waskept at 1.1 bara. After all the propylene had been added, the reactionmixture was held at 130° C. until the pressure reached a constant value.

The reactivity is defined as the time required to propoxylate G670 to apolyol with a molecular weight of 3000 (G3000) at 130° C. and at apropylene oxide pressure of 1.1 bara with 20 ppm catalyst (based on endproduct).

The reactivity in this example was 91 minutes.

COMPARATIVE EXAMPLE 1

Example 1 was repeated except that the viscous, white coloured, stabledispersion of DMC complex particles in a water/tert-butyl alcohol phaseobtained after Procedure A were not subjected to the extractiontreatment (Procedure B) as described in Example 1, but instead weresubjected to a centrifugation treatment (500 rpm, 4800 G) for 1.5 hour,followed by decantation. The catalyst cake obtained was subsequentlyreslurried in tert-butyl alcohol/water (70/30 w/w) mixture andcentrifuged and decanted again. The settled material was re-slurried inpure tert-butyl alcohol, centrifuged and decanted. Finally, the obtainedmaterial was re-slurried in 19 times its amount of G670. After stirringfor a further 30 minutes, the tert-butyl alcohol and residual water wereremoved by stripping under reduced pressure (300 mbar) at 60° C. untilthe water content of the DMC/G670 mixture was less than 0.5 wt %.

The product was a highly viscous, stable, white coloured dispersioncontaining 5 wt % DMC catalyst particles dispersed in G670.

The method used in this comparative example is rather cumbersome andparticularly the decantation and filtration are not suitable forapplication on a commercial scale.

COMPARATIVE EXAMPLE 2

Example 2 was repeated, but this time using the DMC catalyst dispersionof Comparative Example 1.

The reactivity was 109 minutes.

When comparing Example 2 with Comparative Example 2, it can be seen thatthe DMC catalyst preparation of the invention as exemplified in Example1 results in a DMC catalyst which is even better than the DMC catalystprepared to a conventional method as exemplified in ComparativeExample 1. Accordingly, the method of the invention involving stepswhich can be applied on an industrial scale (contrary to the decantationand filtration treatments illustrated in Comparative Example 1) resultsin an excellent catalyst.

EXAMPLE 3 Extracting Liquids

In each of the experiments listed below a certain amount of extractingliquid was added to the aqueous dispersion obtained in Example 1,Procedure A, at room temperature. The amount of extracting solvent addedwas 5, 10, 15 or 20% by weight based on the weight of aqueou dispersionto which it was added.

It was investigated at what amount phase separation occurred with theDMC complex being extracted from the aqueous phase into the extractingliquid phase. The room at which the occurrence of phase separation atroom temperature was observed is indicated in Table I. I: case phaseseparation occurred at a deviating temperature this is explicitlymentioned.

From Table I it can be seen that several different compounds aresuitable extracting liquids for use in the DMC catalyst preparationmethod of the present invention

TABLE I Extracting liquids Exp. Extracting liquid Phase separation 1dichloromethane 10% (5% at 40° C.) 2 2-butyl-2-ethyl-1,3-propanediol 5%3 diethylether 10% 4 methyl tert-butyl ether 10% (5% at 40° C.) 5tert-amyl methyl ether 5% 6 di-isopropylether 5% 7 heptane 10% (5% at40° C.) 8 benzonitril 5% 9 pivalonitril 5% 10 ethyl formiate 20% 11ethyl acetate 15% 12 ethyl 2-ethyl-3-methylbutanoate 5% 13 butylcarbamate 10%

What is claimed is:
 1. A process for the preparation of a DMC catalyst,which process comprises the steps of (a) combining an aqueous solutionof a metal salt with an aqueous solution of a metal cyanide salt andreacting these solutions, wherein at least part of this reaction takesplace in the presence of an organic complexing agent, thereby forming adispersion of a solid DMC complex in an aqueous medium; (b) combiningthe dispersion obtained in step (a) with a liquid, which is essentiallyinsoluble in water and which is capable of extracting the solid DMCcomplex formed in step (a) from the aqueous medium, and allowing atwo-phase system to be formed consisting of a first aqueous layer and alayer containing the DMC complex and the liquid added; (c) removing thefirst aqueous layer; and (d) recovering the DMC catalyst from the layercontaining the DMC catalyst.
 2. The process as claimed in claim 1,wherein the organic complexing agent is tert-butyl alcohol ordimethoxyethane.
 3. The process as claimed in claim 1, wherein theliquid comprises a compound of the general formula (I)

wherein: R¹ represents hydrogen, an aryl group, a substituted orunsubstituted C1-C10 alkyl group or a group R³—NH—, R² representshydrogen, an optionally halogenated C1-C10 alkyl group, a group R³—NH—,a group —R⁴—C(O)O—R⁵ or a cyanide group, R³ represents hydrogen or aC1-C10 alkyl group, R⁴ represents a substituted or unsubstitutedalkylene group having 2 to 15 carbon atoms, R⁵ represents hydrogen, asubstituted or unsubstituted C1-C10 alkyl group, and n and mindependently are 0 or
 1. 4. The process as claimed in claim 3, whereinin the general formula (I) R¹ represents hydrogen, m=1, n=0 and R²represents a group —R⁴—OH with R⁴ representing an alkylene group having3 to 10 carbon atoms.
 5. The process as claimed in claim 3, wherein inthe general formula (I) R¹ and R² independently represent an alkyl grouphaving 1 to 5 carbon atoms, m=1 and n=0.
 6. The process as claimed inclaim 5, wherein the compound of general formula (I) is selected fromdiethyl ether, methyl tert-butyl ether, di-isopropyl ether and dibutylether.
 7. The process as claimed in claim 3, wherein in the generalformula (I) R¹ represents an alkyl group having 1 to 6 carbon atoms,m=1, n=1 and R² represents hydrogen or an alkyl group having 1 to 6carbon atoms or a group —R⁴—C(O)O—R⁵ with R⁴ being a substituted orunsubstituted alkylene group having 3 to 15 carbon atoms and R⁵ being analkyl group having 1 to 5 carbon atoms.
 8. The process as claimed inclaim 7, wherein the compound of general formula (I) is selected fromethyl formiate, ethyl acetate, ethyl-2-ethyl-3-methyl butanoate,di-ethyl malonate and di-ethyl-2-cyclohexyl-2-propyl malonate.
 9. Theprocess as claimed in claim 3, wherein in the general formula (I) R¹ andR² independently represent an alkyl group having 1 to 5 carbon atoms,m=0 and n=0.
 10. The process as claimed in claim 3, wherein in thegeneral formula (I) R¹ represents an aryl group or an alkyl group having1 to 5 carbon atoms, R² represents a cyanide group, m=0 and n=0.
 11. Theprocess as claimed in claim 3, wherein in the general formula (I) R¹ andR² independently represent a group R³—NH— with R³ being hydrogen or aC1-C10 alkyl group, m=0 and n=1.
 12. The process as claimed in claim 3,wherein in the general formula (I) R¹ represents hydrogen, R² representsa halogen-substituted C1-C5 alkyl group, m=0 and n=0.
 13. The process asclaimed in claim 1, wherein step (d) comprises the steps of (d1)admixing organic complexing agent and water with the layer containingthe DMC catalyst and allowing a two phase system to be formed consistingof a second aqueous layer and a layer containing the DMC catalyst; (d2)removing the second aqueous layer; (d3) optionally repeating steps (d1)and (d2) one to five times; (d4) adding organic complexing agent tolayer containing the DMC catalyst while stirring; and (d5) removing thecomplexing agent and recovering the DMC catalyst as solid particles. 14.The process as claimed in claim 1, wherein step (d) comprises the stepsof: (d1) admixing organic complexing agent and water with the layercontaining the DMC catalyst and allowing a two phase system to be formedconsisting of a second aqueous layer and a layer containing the DMCcatalyst; (d2) removing the second aqueous layer; (d3) optionallyrepeating steps (d1) and (d2) one to five times; (d4) adding organiccomplexing agent to layer containing the DMC catalyst while stirring;(d5) adding a liquid polyol to the product of step (d4), thereby forminga slurry of DMC catalyst in a liquid medium of polyol/organic complexingagent; (d6) removing the organic complexing agent; and (d7) recoveringthe DMC catalyst as a suspension in the liquid polyol.
 15. A catalystobtainable by a process comprising the steps of: (a) combining anaqueous solution of a metal salt with an aqueous solution of a metalcyanide salt and reacting these solutions, wherein at least part of thisreaction takes place in the presence of an organic complexing agent,thereby forming a dispersion of a solid DMC complex in an aqueousmedium; (b) combining the dispersion obtained in step (a) with a liquid,which is essentially insoluble in water and which is capable ofextracting the solid DMC complex formed in step (a) from the aqueousmedium, and allowing a two-phase system to be formed consisting of afirst aqueous layer and a layer containing the DMC complex and theliquid added; (c) removing the first aqueous layer; and (d) recoveringthe DMC catalyst from the layer containing the DMC catalyst.
 16. Aprocess for the polymerization of alkylene oxides, which processcomprises polymerizing an alkylene oxide in the presence an a hydroxylgroup-containing initiator and a DMC catalyst obtained by a processcomprising the steps of: (a) combining an aqueous solution of a metalsalt with an aqueous solution of a metal cyanide salt and reacting thesesolutions, wherein at least part of this reaction takes place in thepresence of an organic complexing agent, thereby forming a dispersion ofa solid DMC complex in an aqueous medium; (b) combining the dispersionobtained in step (a) with a liquid, which is essentially insoluble inwater and which is capable of extracting the solid DMC complex formed instep (a) from the aqueous medium, and allowing a two-phase system to beformed consisting of a first aqueous layer and a layer containing theDMC complex and the liquid added; (c) removing the first aqueous layer;and (d) recovering the DMC catalyst from the layer containing the DMCcatalyst.